The separation of fluorescence and elastic scatter/reflection components of fluorescing materials illuminated by white light (or sunlight) is of interest for a variety of environmental remote sensing, medical diagnostics, and colorimetry applications. These include the study of upwelling radiation from algae in sea water, where the magnitude of the fluorescence peak can be considered as a measure of chlorophyll concentration and photosynthetic activity, as described in A. A. Gitelson, et al., “Remote Estimation of Chlorophyll Concentration in Productive Waters: Principals, Algorithm Development and Validation,” Proc. of NWQMC, 149 (2000). Applications also include the examination of coral reefs containing fluorescing pigments, as described in J. F. R. Gower, et al., “Interpretation of the 685 m Peak in Water-Leaving Radiance Spectra in Terms of Fluorescence, Absorption and Scattering, and its Observation by MERIS,” Int. J. Rem. Sens., No. 20, 1771 (1999).
A variety of techniques have been used to effect this separation in experimental measurements. Dual monochromator techniques utilize monochromatic sources and detectors which must be carefully and selectively tuned over appropriate spectral ranges to measure true elastic reflectance, as discussed in F. Grum, “Colorimetry of Fluorescent Materials,” Optical Radiation Measurements, Vol. 2, Chap. 6 (Academic Press, New York, 1980). Other techniques use a series of bandpass filters to separate elastic and inelastic components. These methods are particularly effective where the fluorescence is characterized by large Stokes shifts, but involve a complicated multiple-step procedure.
A recent approach, which is described in E. Fuchs, “Separating the Fluorescence and Reflectance Components of Coral Spectra,” Appl. Opt. No. 40, p. 3614 (2001), makes use of measurements with and without sharp long pass filters to permit in-situ measurements and separation of elastic reflectance and fluorescence from coral reefs.
There is a need, therefore, for a simple and accurate method and apparatus that provide the separation of fluorescence components from the elastic reflection components in the reflectance spectra of an illuminated object.